Telephone system



1935 B. G. DUNHAM 2,023,011

TELEPHONE SYSTEM Filed May 22, 1954 is?" "H? M INVENTOR B. G. DUNHAM ATTORNEV Patented Dec. 3, 1935 UNITED STATES PATENT OFF TELEPHONE SYSTEM Bert G. Dlinham, Hawthorne, N. J., assignor to Bell Telephone Laboratories, Incorporated, New

York, N Y

a corporation of New York Application May 22, 1934, Serial No. 726,889 10 Claims. (Cl. 179-16) when employed in automatic and semi-automatic telephone systems.

The objects of this invention are to increase the release of the equipment, and to otherwise improve systems of this character.

Impulse repeaters have been devised heretoawaits the closed period following the open period of the incoming Arrangements have also been made for correcting the repeated impulses to compensate for vices which send the impulses at a relatively fast rate and by transmitting devices which send impulses at a relatively slow rate.

than a certain, minimum value. This requires that the outgoing circuit, once opened, be held opened under the control of time measuring sponds to the incoming impulses. the outgoing circuit is reclosed at If, however, the end of circuit and a release signal which should merely open the outgoing circuit without causing its reclosure.

station. A line-finder LF has access of lines including the line to which is connected. Selectors SI, S2, S3

to groups station A 35 circuit IR is shown in detail. 40 The subscribers stations A and B are provided with the usual subscribers set with a dial for controlling the establishment of desired connections.

those portions of the circuits of the line-finder, selector and connector switches are shown as is required for a clear and complete description of this invention, the omitted portions of these circuits being represented by broken lines.

The incoming repeater IR is shown in detail and is associated with the interofiice trunk 5 to repeat the impulses for establishing the remainder of the connection after the calling line has been extended 'to this repeater circuit. The operation of this circuit is fully set forth in the following description of a call from station A to station B.

When the receiver is removed from the receiver hook at station A to originate a call, the line-finder LF hunts for and extends the line I through its multiple brushes 2 to the first selector SI. When the calling subscriber dials the first digit of the called subscribers number, the brushes 3 of selector SI are advanced to a corresponding group of terminals. The selector SI then automatically hunts for and seizes an idle set of terminals in the selected group to extend the line I to the second selector S2. When the calling subscriber dials the second digit of the called subscribers number, the brushes 4 of selector S2 are advanced to a corresponding group of terminals. The selector S2 then automatioally huntsfor and seizes an idle set of terminals in the selected grou Assume that the selected set of terminals is connected to the incoming trunk 5 which is associated with the incoming repeater IR. A circuit is thereby closed to operate relays 6 and 1 from ground, through upper windings of relays ,6 and 1, resistance 2|, lower left winding of repeating'coil 25, lower back contact of relay I9, tip conductor, of trunk 5, tip terminals and brushes of selectors S2 and SI, tip terminal and brush of line-finder LF, tip conductor of line I, through the subscribers instrument at station A, ring conductor of line I, brush and ring terminal of line-finder LF, brushes and ring terminals of selectors SI and S2, ring conductor of trunk 5, upper back contact of relay I9, upper left winding of repeating coil 20, resistance 22, lower winding of relay 1 and thence through the middle winding of relay 6 to battery. Relay 6 (and this is also true of relays I3 and 21 later to be mentioned) is of the type wherein a permanent magnet is employed and wherein an electrical means of biasing is used for restoring the armature to normal rather than the usual mechanical means. Relay 1 closes a circuit through both windings of the electric-ally biased relay 21. This circuit may be traced from ground at back contact of relay 8, front contact of relay 1, ductor 25, thence in parallel, one path extending through right winding of relay 21, resistance 34 and thence through resistance 35 to battery, and the other extending through left outer back contact, of relay I1, right back contact of relay II and through the left winding of relay 21 to battery. The current through the left winding of relay 21 electromagnetically opposes the current through its right winding .so that the resulting bias will restore this relay to normal, if operated. Relay 1 also closes an obvious circuit through resistance 23 and the lower. winding of relay 6 to battery for the purpose of effecting an electrical bias on relay 5 thereby insuring its release .when its operating circuit is opened.

Relays 3 and 1 operated close a circuit for energizing relay 9. This circuit may be traced from back contact of relay ground at the back contact of relay 8, front contact of relay 1, conductor 25, left inner back contact of relay I1, front contact of relay 6, conductor 2t, and thence through the back contact and winding of relay 9 to battery. The operation of relay 9 closes an obvious circuit for the energization of slow-to-release relay I5, removes the short-circuit from resistance 24 and connects the winding of relay I1 to conductor 26 in a circuit traced from conductor 26, left front contact of relay 9, winding of relay I1, back contact of relay 21 and'thence to ground on conductor 25 as aforementioned. Relay I5 is slow-to-release and is so designed that it will not release when its circuit is momentarily opened during the transmission of outgoing impulses. Resistance 24 is provided for the purpose of reducing the voltage across relay 9 after its back contact is opened. This resistance is normally short-cir cuited in order that the full voltage of the central ofiice battery may be impressed across the winding of relay 9 to accelerate its operation. Relay I1 does not operate in the aforementioned circuit since its winding is short-circuited by ground on conductor 26. The operation of slowtorelease relay I5 connects ground to conductor 25 thereby supplementing the aforementioned ground on this conductor, connects ground to the sleeve brush 33 of selector S3, closes an energizand closes a bridge to the line relay (not shown) of selector S3. This latter circuit may be traced from brush 28 of selector S3, tip conductor 3 I, back contact of relay I4, back contact of relay I2, lower right winding of repeating coil 20, through resistance '35 and relay I8 in parallel, upper right winding of repeating coil 29, ring conductor 32, upper front contact of relay I5 and thence to brush 29 of selector S3. The polarized relay I8 does not operate at this time since the current through its winding is flowing in. the wrong direction. Relay I3 is energized in a circuit from ground at lower outer front contact of relay I5, right winding of relay I3 and through resistance 33 to battery. Relay its is energized in a circuit from ground at lower middle front contact of relay I5, left inner I2 and through left winding of relay IE to battery.

The operation of relay I3 provides an obvious short-circuit for relay i2 and opens the operating circuit for relay I l. Relay I0 operated shortcircuits resistance 34 for the purpose of altering the operating time of relay 21 for the first digit dialed into the repeater as will be explained later.

When the impulses corresponding to the third digit of the called number are dialed, relay 6 is alternately released and reoperated. Relay 1 may or may not release during the transmission of impulses. Its function is immaterial following the operation of relay I5 since the latter relay now furnishes a ground on conductor 25 for holding the repeater. Each release of relay 6 opens the aforementioned short-circuit from relay I1 thereby causing its operation in a circuit from ground on conductor 25, right back contact of relay 21, through winding of relay I1, front contact of relay 9, resistance 24 and through the winding of relay 9 to battery. Relay 9 also remains operated in this circuit. Relay I1 operated removes ground from the armature of relay 6 and closes a circuit through the left winding of relay I3. This circuit may be traced from ground on conductor 25, left inner front contact of relay I1, conductor 35 and through the left winding of relay I3 to battery. The current through the left winding of relay l3 electromagnetically opposes the current through its right winding thereby causing the release of relay H3. The aforementioned ground on conductor 36 also provides a discharging path for condenser 3? through ll opens the aforemenleft winding of relay 2? thereby causing the operation of relay 27 after a predetermined time interval. When the circuit, through the left winding of relay 2?, is opened,

start to charge in an obvious circuit. This charging current will maintain relay 2? released until said charging current has such that the difference beresistances 3d, 35 and it and condenser 39 are so chosen that a predetermined operating and the other extending through right front contact and winding of relay iii to battery. Relay it also closes a circuit in parallel with the lower back contacts of relay Id.

The release of relay 13 front contact of relay l2 and through the winding of relay [5 to battery, removes the shortcircuit from resistance 22 and short-circuits the ing the pulsing loop. The operation of relay H removes the shunt consisting of resistance 513 from the winding of relay ll.

When relay 2'! operated, it opened the aforementioned circuit for relays 9 and i7 thereby causing the release of said relays. The release of relay 9 short-circuits resistance 2 to accelercontact to the armature of relay 6, opens the left winding (release) of relay 5% thereby causing the reoperation of relay it after a predetermined .held operated during the pulsing period,

'3 condenser 31 are so chosen that a predetermined operating time is obtained for relay l3. Relay l? released, opens the operating circuit for relay H and the holding circuit for relay Ill, thereby series to line relay (not shown) of selector 83. This circuit, as initially traced, was completed through the back contacts of relay I 4 and subsequently through the right front contacts of relay 9 i which parallel the back contacts of relay Hi. The aforementioned operation of relay I l transferred the control of the outgoing pulsing or dialing circuit to relay l1.

then initiates the open period of the first repeated pulse to operate selector S3. Condenser t8 and resistance 49, shown bridged across the back contacts of relay I 1 and the right front contacts of relay H, are provided to improve pulsing.

The release of relay H discharges condenser 39 in a circuit traced from ground at condenser 39, resistance 46), right back contact of relay 8 I and thence to aforementioned ground on conductor 25. Relay ll released recloses the circuit through the left winding of relay '21, thereby causing the release of this relay as aforemenbe described presently, relay It can not reoperate and therefore the right winding of relay Hi is not included in the subsequent operating circuit for relay It.

Thus, resistance selector and connector the impulse frequency is high.

ping of the succeeding switches when Relay is so that its operating time plus the releasing time of relay M will insure an opening of the isfactory stepping of the succeeding selector and connector switches when the impulse frequency is low. When impulses are being received by is also designed and electrically biased ll, reoperates relay H3,

4- relay 6 at a low rate of impulses per' second, the open periods constitute such a small part of each impulse cycle that it is necessary to provide a fixed minimum allowable open period for each impulse in order that the line relay (not shown) of the switch to which the impulses are being transmitted will not be in an operated position long enough to cause a failure of the switch. The minimum allowable open period of each impulse is determined by the operating time of relay l3 and the releasing time'of relay M. This timing is accomplished as follows: When relay 6 reoperates, following the first impulse, relay 9 reoperates, but before relay it releases on the succeeding impulse relay it has had sufficient time to operate thereby releasing relay id. Relay M released recloses the bridge thus terminating the open period of the previous outgoing impulse independently of relay ll. At higher impulsefrequencies each impulse cycle is shorter and, if the frequency exceeds a certain value, the open periods (as measured by relays i3 and. I4) constitute such a large part of each impulse cycle that it is necessary to control the bridge closure independently of relays l3 and M in order that the line relay (not shown) of the switch to which the impulses are being transmitted will not be in a non-operated pos tion long enough to cause a failure of the switch. The frequency at which the closed period is barely sufficient to prevent a failure of the switch receiving the impulses when the open period is controlled by relays l3 and I4 is a critical frequency. At frequencies higher than the critical frequency the minimum allowable closed period of each impulse is determined by the operating time of relay 2? and the releasing time of relay M. This timing is accomplished as follows: When relay 6 reoperates following the first impulse, relay 9 reoperates and when relay 5 releases on the succeeding impulse, relay ll operates to reclose the releasing circuit for relay l3 before this relay has had time to operate. during the transmission of impulses and relay I'I recloses the bridge to terminate the open period of the previous impulse independently of relay I l. Thus it is seen that when the impulse frequency is low, the open period of the outgoing pulse is timed and that when the impulse frequency is higher than the critical frequency, the closed period of the outgoing pulse is timed thereby correcting the outgoing pulses for satisfactorily controlling the stepping of the succeeding selector and connector switches.

On the last impulse of each digit dialed, relay l3 operates thereby releasing relay l2. Relay l2 removes the holding ground for relay l5 which wil now be held operated under control of relay removes the short-circuit from the right windings of repeating coil Zliand V short-circuits resistance d2,

The alternate closing and opening of the bridge across conductors 3i and :32 as aforementioned, causes the associated selector S3 to function in the usual manner to select an idle trunk terminating in selector S i. When the calling subscriberdials the remaining digits of the called stations number, the selector S4 and the conmotor are operated to extend the connection to line as with when station B is associated. When the called subscriber removes the receiver at station B in answer to the usual ringing signal, the connector C operates in the usual manner to reverse the current flowing through the polarized relay; P8 in the incomingrepcater'IR. Relay l8 Relay 54 therefore remains operated.

operates when the current is reversed thereby causing the operation of the reversing relay IS in a circuit traced from ground at lower outer front contact of relay l5, front contact of relay [8 and through the winding of relay l9 to bat- '5 tery. Relay l9 reverses the connections from the conductors of trunk 5 with respect to the windings of relay 6 so that the current is re versed over the conductors of trunk 5 to signal the operator or .to initiate the operation of the charging meter (not shown) associated with the calling subscribers line I. The talking circuit extends through the repeating coil 20 and the talking condensers 45.

When the connection is released by the calling 15 subscriber, relay 6 releases thereby causing the operation of relay I! in series with relay 9. Relay l'i releases relay l3, removes ground from the armature of relay 6, opens the release circuit of relay 2'? thereby causing said relay to operate 2 after an interval of time, operates relay H and closes a circuit in parallel with the back contacts of relay l4. Relay l3 released, causes the operation of relays l2 and I4, Relay I4 closes a circuit for holding relay at lower middle contact of relay l5, back contact of relay l3, front contact of relay M and through lower outer front contact and winding of relay it to battery. The operation of relay l2 holds relay it: operated and short-circuits the right 30 windings of repeating coil and winding ofrelay l8 thereby causing the release of said relay. Relay l8 released, operates relay 8 in a circuit traced from aforementioned ground at lower front contact of relay 2, back contact of relay l8 and 35.

through windingv of relay 8 to battery. When relay 21 operates, it releases relays 9 and H. Relay I! released, opens the bridge across conductors 3i and 32-, reconnects ground to the armature of relay 6, causes relay [3 to operate 40 after a time interval and releases relays l0 and H. Relay I! released, releases relay 2-1. Relay l3 reoperated, releases relay l2 and opens the operating circuit for relay Hand the holding circuit for relay l9. operated under control of relay l5 from ground on conductor 25, left inner. back contact of relay ll, back contact of relay 6, thence in parallel, one path extending through the lower outer front contact and winding of relay L9 to battery, and 50 the other extending through the front contact and winding of relay M to battery. The release of relay l2 releases slow-to-release relay l5 which removes ground from the sleeve conductor of selector S3 and releases all other operated relays. In this manner the repeater is able to distinguish between an open condition of the incoming circuit caused by the transmission of an impulse which is followed by a closure of the incoming circuit and an opening of the incoming 60 circuit caused by the release of the calling subscriber or operator, in which case the incoming circuit is not reclosed. Relay 8 is slow-to-release and disconnects ground from the armature of relay 1 for a sufficient length of time to .prevent the momentary reoperation of relays 6 and i from simulating a reseizure of the repeater by selector S2. This momentary operation of relays 5 and l is caused by a momentary short-circuit across the tip and ring conductors, associated 70 with the left windings of repeating coil 20 when relay it releases. The release of relay 8'restores the circuit to normal ready for seizure on an other call.

The features of this inventionare not limited";

It operated from ground 5.

However, these relays are held 45 in their application to an incoming repeater circuit but may also be incorporated in outgoing repeaters as well.

What is claimed is:

1. The combination in a repeating mechanism of an incoming circuit and an outgoing circuit, means for opening and closing the incoming circuit to send an impulse to said mechanism, means responsive to the opening of the incoming circuit for causing the opening of said outgoing circuit, time measuring means for maintaining said outgoing circuit open not less than a predetermined interval of time, and means dependent on the condition of the incoming circuit for holdingopen said outgoing circuit beyond the termination of said predetermined interval.

2. The combination in a repeater of an incoming line and an outgoing line, impulse transmitting means for opening and closing said incoming line, means responsive to the opening of the incoming line for causing the opening of said outgoing line to transmit an impulse thereover, timing means for holding open said outgoing line for a period of time not less than a predetermined interval, and means for preventing the reclosure of said outgoing line until said incoming line has reclosed.

3. The combination in a repeating mechanism of an incoming circuit and an outgoing circuit, means for opening and closing the incoming circuit to send impulses therein, means responsive to the opening of the incoming circuit for causing the opening of said outgoing circuit at a given point, means for closing said outgoing circuit at another point, timing means for insuring of said outgoing circuit shall not be less than a predetermined interval, and means effective if the incoming circuit has not reclosed at the end of said predetermined interval for maintaining said outgoing circuit open.

4. The combination in a repeater of an incoming line, an impulse receiving relay for said incoming line, means for opening and closing the incoming line to operate said impulse receiving relay, a second relay responsive to the impulse receiving relay when the incoming line is opened for opening said outgoing line, timing means for reclosing said outgoing line at the end of a predetermined interval after the opening thereof by said second relay, and means controlled by said impulse receiving relay if said incoming line is not reclosed prior to the expiration of said predetermined interval for maintaining said outgoing line open until the closure of said incoming line.

5. The combination in a repeating mechanism of an incoming circuit and an outgoing circuit, means for opening and'closing the incoming circuit to transmit impulses, two control contacts for said outgoing circuit, means an incoming impulse for opening one of said contacts to open the outgoing circuit, means for closing the other of said contacts to reclose said outgoing circuit, and means eifective in response to a change in the speed of said incoming impulses for holding said second contact open and for rendering said first contact effective both to open and close said outgoing circuit.

6. The combination in an impulse repeater of an incoming line, means for opening and closing said incoming line at varying rates of speed to send impulses thereover, an outgoing line, two separate circuits for closing said outgoing line, 5 means responsive to an incoming impulse for for holding said second circuit open and for rendering said first circuit eifective both to open and to close said outgoing line. 15 7. The combination in an impulse repeating mechanism of an incoming line and an outgoing impulses thereover, two separate control circuits 20 for opening and closing said outgoing line, means efiective when impulses are transmitted at a fast ing and closing impulses thereover to said repeater, means responsive to the opening of the incoming circuit for measuring a predetermined interval regard- 60 less of the rate at which impulses are sent by BERT G. DUNI-IAM. 

